Studies of cardiopulmonary receptors with vagal or sympathetic afferent limbs have indicated that these receptors have a number of significant reflex effects on the circulation and respiration. These receptors are located within the atria, ventrals, pericardium, lung vasculature and lung parenchyma. The distribution of these afferents arising from the nodose ganglion or dorsal root ganglion of each spinal segment is not clearly known. The level of afferent ingegration for these reflexes is also unknown and needs to be explored. These studies using ganglion injections of tritiated leucine and autoradiography as a neuroanatomical tracing technique will be used to define the distribution both the spinal segment and vagal afferent fibers as well as their fiber types and relative numbers of each. Individual receptors will also be located and their firing characteristics studied along with electromicroscopic examination of their structure. Activation of these cardipulmonary afferents using physiological and electrical stimulation have produced reflex changes in blood pressure, i.e. depressor and pressor responses, heart rate, and respiration, i.e. apnea, tachypnea and bradypnea. The interaction of these various reflex rexponses needs to be defined as well as the definition of the adequate physiological stimulus for these receptors.